1. Field of the Invention
This invention relates generally to a tape cassette for use in tape recording and reproducing apparatus, and more particularly is directed to a tape cassette having a safety device adapted to control the recording circuit of the apparatus for preventing inadvertent erasure of previously recorded information on the tape in such cassette.
2. Description of the Prior Art
Tape cassettes of the above described type have previously been proposed which include an integral safety device adapted to prevent inadvertent erasure of previously recorded information on the tape contained within the cassette. In the well known "Phillips" type cassette, such safety device is constituted by a frangible tab which normally extends across an aperture in the peripheral wall of the cassette housing and which is adapted to be engaged by the actuating element of a microswitch in the tape recording and reproducing apparatus when the cassette is disposed at an operative station in such apparatus. The microswitch controls the recording circuit of the apparatus and, when its actuating element is engaged by the tab on a cassette, the microswitch completes the recording circuit so that new information may be recorded on the tape in such cassette or previously recorded information may be erased from the tape. When it is desired to retain the information recorded on the tape and prevent erasure thereof, the tab may be removed so as to leave the respective aperture unobstructed. In that case, when the cassette is disposed at the operative station within the recording and reproducing apparatus, the actuating element of the microswitch can enter the unobstructed aperture with the result that the microswitch maintains the recording circuit of the apparatus in its inoperative mode and, therefore, it is impossible to record over the previously recorded information and/or to erase such information from the tape. While cassettes of the "Phillips" type have been generally satisfactory, it is to be noted that, once the tab is broken or removed from a cassette, it is no longer possible to re-record information on the tape in such cassette. Therefore, in the event that the information recorded on the tape should subsequently become dispensable, the cassette and the tape therein must either be disposed of, or the cassette housing repaired with considerable difficulty so as to replace the tab thereon. Further, due to the location and configuration of the frangible tabs on such cassettes, consumers frequently experience difficulty in removing the tab from a cassette.
In order to avoid the foregoing problems associated with the described safety device of the "Phillips" type cassette, it has been proposed, for example, as disclosed in detail in U.S. Pat. No. 3,721,772, issued Mar. 20, 1973, and having a common assignee herewith, to provide a cassette with a safety device in the form of a flat disc having a recess therein which is offset from the central axis of the disc, and with the disc being removably mounted on the cassette housing so as to be selectively disposed in one or the other of two positions which are turned 180.degree. relative to each other. With the foregoing safety device, in one position of the disc on the cassette housing, the actuating element of the microswitch engages the flat surface of the disc so as to cause the microswitch to complete the recording circuit and permit recording of information on the tape within the cassette. In the other position of the flat disc constituting the safety device, the actuating element of the microswitch can engage in the recess of the disc so that the microswitch maintains the recording circuit in its inoperative mode for preventing inadvertent erasure of previously recorded information on the tape. Although the foregoing safety device constituted by a removable disc substantially avoids the above described problems associated with the safety device of the "Phillips" type cassette, there is the danger that the removable disc may be accidentally removed or separated from the cassette housing during storage or transportation of the cassette, in which case a new disc has to be installed on the cassette housing and may be incorrectly positioned so as to permit erasure of previously recorded information which is to be preserved.
Still another proposed safety device for a tape cassette, for example, as disclosed in detail in U.S. Pat. No. 3,828,363, issued Aug. 6, 1974, is constituted by a slide member which is movable longitudinally in a slot defined in the peripheral wall of the cassette housing so as to be selectively disposable in one or the other of two positions in which the slide member respectively blocks and unblocks the opening to a recess formed in the peripheral wall. Thus, when the slide member is positioned to block the opening to the recess, the actuating element for the microswitch engages the slide member so as to obtain the operative mode of the recording circuit, whereas, when the slide member is positioned to unblock the recess, the actuating element of the microswitch can enter the recess and thereby maintain the recording circuit in its inoperative mode for preventing erasure of previously recorded information on the tape. The foregoing safety device is disadvantageous in that the slide member can be inadvertently displaced from one to the other of its two positions when handling or storing the cassette, with the result that the slide member will thereafter either prevent recording of information on a tape which has not been previously recorded or which contains information that need not be preserved, or will permit the erasure of recorded information that should be preserved.